Category: SQL Server

SQL Server Environmental Diagnostics Guide

SQL Server Environmental Diagnostics Guide

Jeff Mlakar12 Comments

Supporting an application as a DBA means you have encountered complaints about performance. The investigation starts and the root cause must be determined. Often times the end result is not a bug in the code but rather something specific to the environment. Environmental problems are usually the culprit.

Performance problems for a SQL Server based application are likely to be caused by environmental factors and not buggy code.

Whether it is a configuration you can change in SQL Server, Windows Server, VMware, or the network it is likely the first course of action is to perform a quick assessment of the environment. This is where understanding the various configurations and best practices are key. Knowing what to look for can save tons of time.

A mistake I often see is a performance issue is passed off to someone else (more senior) and that engineer assumes a lot of things without checking. People are going to relay the problem as they see it – not as it actually is. This leads to skipping over some elementary checks which can save time and frustration from tracking down imaginary bugs.

Start troubleshooting with a quick environmental check.

Below are common environmental mishaps I see when troubleshooting SQL Server performance complaints. Consider these 1st line of action before getting into execution plans, statistics, indexing, and code refactoring.

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SQL Saturday – Raleigh 2017 – Amazing Professional Community

SQL Saturday – Raleigh 2017 – Amazing Professional Community

Jeff Mlakar2 Comments

This Saturday was SQL Saturday for Raleigh. Attendance was strong, classrooms were filled, and the event was a success. When I attend these events it amazes me how strong the SQL community is. Speakers travel from states away, volunteers setup and plan the event, vendors sponsor the event and meet at their booths with participants, and people come to learn on an Saturday.

That really says something about SELECT individuals who INNER JOIN with each other ON a Saturday WHERE the goal is to learn from each other as a GROUP BY sharing knowledge we are lucky enough HAVING such a great community. I’ll stop now in ORDER to show some pictures of day!

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Using T-SQL to Insert, Update, Delete Millions of Rows

Using T-SQL to Insert, Update, Delete Millions of Rows

Jeff Mlakar4 Comments

Challenges of Large Scale DML using T-SQL

Using T-SQL to insert, update, or delete large amounts of data from a table will results in some unexpected difficulties if you’ve never taken it to task.

Let’s say you have a table in which you want to delete millions of records. If the goal was to remove all then we could simply use TRUNCATE. However, if we want to remove records which meet some certain criteria then executing something like this will cause more trouble that it is worth.

Why not run the following in a production environment?

  • Transaction log growth – expect a large transaction like this to cause the transaction log to expand. Calls to expand the database files are some of the most expensive operations SQL Server makes to the OS. Hopefully the initial sizing was good and the growth settings are reasonable.
  • Blocking – concurrency is going to increase the likelihood of lock escalation. That will lead to the possibility of excessive blocking.
  • Rollbacks – if the SPID is killed then the transaction will enter a rollback state. For very large transactions this can take a lot of time. Don’t even think about killing or stopping SQL Services during a rollback unless you want a corrupt database!

What can we do to improve this?

We follow an important maxim of computer science – break large problems down into smaller problems and solve them.

We break up the transaction into smaller batches to get the job done. Each of the above points can be relived in this manner. Let’s take a look at some examples.

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